/Engine/Source/Developer/PakFileUtilities/Public/PakFileUtilities.h
Add the given filename with the given Offset interpreted as Offset in bytes in the Pak File. This version of Add is only useful when all Adds are done by offset, and are converted into Sorting Indexes at the end by a call to ConvertOffsetsToOrder
void AddOffset ( const [FString](API\Runtime\Core\Containers\FString) & Filename, uint64 Offset )